warning: this video deals with corrosive and volatile acids. toxic gases and toxic chemicals. wear gloves when handling them and work outside or in a fume hood. greetings fellow nerds. in a previous video we processed liters of laboratory chemical waste from an organometallic research lab to produce a couple grams of platinum concentrate powder. in this video we're going to try and extract that platinum. first, i need to crush your expectations: the quantities of platinum recovered in this video are not economical to recover at this scale.
if you want platinum, it's cheaper to buy it. this is only economical when working with hundreds of grams of platinum and kilograms of platinum concentrate powder. our objective in this video is to explore the science. i can't believe i still need to keep saying that after all these years. anyway, let's get started. first we get 50ml of concentrated hydrochloric acid. i'm using a 31% solution but the exact concentration is not critical. being plus or minus 10% is fine. now we get our 2.4g of platinum concentrate powder that we collected in a previous video.
if you haven't seen it, click here or in the video description. now dump that right in. for quantitative transfer wash out any dust with water. okay now gently boil and stir the mixture for half an hour or so. what we're doing is dissolving any base metals or base metal oxides in the concentrate. now this step is entirely optional since we're going to go through another base metal remove step later on. in fact for such a small quantity of material this isn't worth it but i'm showing you for those cases where you have large quantities of material. if you have kilograms of platinum concentrate powder then shaving off a few tens of percent can greatly save on expensive nitric acid later on.
okay once it's boiled filter it off. the base metal chlorides like zinc, iron and so on will filter out leaving behind the more noble metals like platinum and copper. now we actually dissolve the platinum metal using aqua regia. first, wash the residue into a beaker using concentrated hydrochloric acid. top up the hydrochloric acid to at least 4ml per gram of residue. i actually have a huge excess since i used a lot more hydrochloric acid just washing out the filter. now add in about 1 ml of nitric acid for every 3 ml of hydrochloric acid you have. now gently heat the mixture to about 95 celsius with stirring.
what's happening is the nitric acid and the hydrochloric acid react with platinum to produce hexachloroplatinic acid. the mixture of nitric and hydrochloric acid is well known for being able to dissolve many precious metals and is even famous enough to have it's own name, aqua regia. anyway, the reaction also produces various nitrogen oxides and nitrosyl chloride gases so this must be performed outside or in a fume hood. you can see it here as that orange brown haze above the reaction mixture. keep heating and stirring until the orange disappears indicating we've depleted the nitric acid. now turn off the stirring and let it cool. now we filter off the mixture.
the filtrate should contain our platinum as well as any other metals that got dissolved and the residue should contain carbon and any unreacted platinum. platinum is quite resistant to aqua regia as i showed in my previous video on dissolving a platinum bar. so to ensure we go complete dissolution, we're going to leach it out a few more times. wash the residue back into the beaker and again run another treatment of 4ml of hydrochloric acid per gram of platinum and 1ml of nitric acid per gram of platinum. once again boil, wait until no more orange gases are produced and then cool and filter. keep repeating this process until the filtrate color is a constant shade of yellow or the stannous chloride test shows no more metals dissolving.
filter everything and wash down the residue, let it dry on the filter under the air stream. now i preweighed this filter so we could compare it to the weight of the loaded filter later. here it is dried. looks like the difference is 1.8g. but the amount of starting platinum concentrate powder was 2.4g. we only dissolved a total 0.6g and we're not even sure if that was all platinum. i was hoping for more of the powder to dissolve but it's clear there is a lot leftover. this powder is mostly carbon. it didn't burn very fast in the crucible because it was it encased in salt and metal oxides.
i didn't give it enough time to eventually burn away. now to get more yield we should put this back into the crucible and since we've leached out all the salts and most of the metals this chemically cleaned carbon should burn quite easily. unfortunately i don't have enough time to again go through the subsequent boiling and leaching steps so i'll set this aside and add it to my future platinum recovery runs. additionally, we did already leach out most of the metals so what platinum remains inside this carbon is probably minimal. for now i'll go ahead with our existing 0.6g of material even though at this point our interest is purely academic. and here is our filtrate from all those aqua regia treatments. yeah i kinda went overboard.
you should not have this much from your runs. first we need to destroy all the leftover nitric acid. so we set up a distillation apparatus with our filtrate in the boiling flask. yeah i learned my lesson from last time and this distillation apparatus should let us boil the filtrate without polluting the atmosphere. just turn it on and start boiling. what we're doing is decomposing any nitric acid still remaining in the filtrate. these will interfere with our separation and recovery of the platinum later so we need to get them out. as the hydrochloric acid in the filtrate distills, it will attain a yellow color as the nitrogen oxides gases and nitrosyl chloride compounds dissolve in it.
keep boiling until we have just 50ml or less of liquid. we should actually be going down to 10ml but that's hard to tell in this large flask. turn off the heating and let it cool. then add an equal volume of hydrochloric acid and start boiling again to below 50ml for another round. if the nitric acid is fully destroyed then the distillate should be clear. since mine is still yellow in this round i'll have to add more acid and boil again. here we are after a third round of boiling and hydrochloric acid addition. finally the distillate is clear indicating we're not generating any new nitrogen oxides. we now boil down to about 10ml.
and here is our solution of very impure hexachloroplatinic acid. now to remove the base metals by alkaline precipitation. transfer the solution to a beaker. mine is a lot more than 10ml now since i washed out the flask with water. nonetheless we can still proceed forward. for every gram of material that was originally dissolved add in an equal amount of sodium chloride salt. since we dissolved 0.6g of metal we add in 0.6 g of sodium chloride. now gently boil down until dry. don't use too high a heat or you'll decompose the platinum salts.
i set my hot plate to a temperature of one hundred twenty celsius. we're basically driving off the last of the hydrochloric acid. we added sodium chloride so that we formed sodium hexachloroplatinate. this stabilizes the platinum as hexachloroplatinic acid decomposes into platinum chloride at high temperature. platinum chloride is difficult to dissolve again, especially in alkaline solutions, now once it's all dry add in 10ml of water for every half gram of material dissolved. then add in 1g of sodium bicarbonate for every half gram of material dissolved. now gently stir and raise the temperature until it just starts to bubble. sodium bicarbonate is alkaline and reacts with the base metals to form insoluble metal carbonates, oxides and hydroxides.
sodium hexachloroplatinate however is still soluble. now these steps are optional if you're refining platinum that you know doesn't have such metals like jewellery or platinum scrap. since i don't know what sort of other metals are present in this platinum, i'm taking the time to do this step to try and remove most of them. okay after the solution is boiling for a few minutes turn off the heating and let it cool. now filter the mixture. if you have a lot of material it might be more prudent to use a buchner funnel with filter paper rather than a glass frit as glass frits tend to clog easily with particles this fine. anyway, after all the material has gone through, you can wash the precipitate with some water.
just for your knowledge, i took the residue on the filter and dissolved it in hydrochloric acid. this material was what didn't go through. as you can see we had quite a bit of base metals that we successfully separated. anyway here is our filtrate, a solution of sodium hexachloroplatinate with sodium chloride but with most of the other metals removed. now if you're certain you don't have other noble metals like gold, or palladium then you can add a reducing agent right here like hydrazine or sodium metabisulfite to reduce the platinum into metal. i can't do that though because i was told by the lab this platinum contains a few percent of palladium. so i have to separate that first. to separate out the platinum from the palladium
we add in a saturated solution of ammonium chloride, about 2-3ml. now if you have larger quantities and need more precision, you add 0.6g of ammonium chloride for every 1g of platinum you expect to recover. give it a thorough shake and let it settle. the bubbling is from carbon dioxide that forms from the ammonium chloride reacting with the leftover sodium carbonate and bicarbonate dissolved in solution. in our intended reaction, ammonium chlorides reacts with sodium hexachloroplatinate to produce insoluble ammonium hexachloroplatinate. we didn't form ammonium hexachloropalladate because hexachloropalladate is unstable at boiling temperatures and would have been reduced to tetrachloropalladate during our many repeated boilings earlier. we can thus separate the two metals now by filtration. wash the ammonium hexachloroplatinate with a 1% solution of ammonium chloride.
let it dry on the filter under an air stream. you can also wash it with ethanol and diethyl ether to achieve greater purity if desired. now this filtrate has some palladium and tiny amounts of leftover platinum. to improve platinum recovery, add in some ammonium chloride solution and look for precipitation. if there is a lot precipitation then you can filter it again and get better recovery. if there is very little, then it's not worth recovering. you can make your own judgement call as to when to stop. to get a perspective of just how little platinum this actually is let me show you this flask which looks like it has a lot of yellow ammonium hexachloroplatinate coating on the inside.
i'm going to reduce it back to platinum metal with some sodium metabisulfite solution. i'm boiling it a bit to speed up conversion, and now i'm adding some hydrochloric acid to dissolve the precipitated sodium sulfite. wait a minute, where's the platinum? all that yellow ammonium hexachloroplatinate amounted to no visible platinum. let me put it on the white hotplate to show you. ammonium hexachloroplatinate has an intense yellow color that can be misleading as to how much platinum you actually have. so while my filtrate looks like a lot, it's actually practically nothing. nonetheless there is some palladium in here, so i'll add this to my stock of precious metals waste for future recovery. to reduce the volume of material i need to store. i'm going to add some zinc metal and cement out all the remaining metals in solution.
i can then filter the residue and store the metals without the salts currently in solution. i'll show you how to recover palladium once i have enough. so here is our dried ammonium hexachloroplatinate and i've transfered to this vial. this can easily be converted back to platinum by simply heating it above 400 celsius. for small quantities its a good idea to dry the material first on the hotplate by heating it up to 200 celsius and boiling the water off. if you heat it to full temperature too fast the sudden boiling of the water can blow apart the ammonium hexachloroplatinate making you lose it. for large quantities in large containers this is less of problem. anyway, what's happening is the ammonium hexachloroplatinate is decomposing into platinum metal, nitrogen gas, hydrogen chloride and ammonium chloride.
now platinum melts at 1768 celsius so at these temperatures we're not going to make a solid piece of platinum. instead we're producing extremely fine platinum particles commonly called platinum sponge. now i'm doing this in a vial to show you the process. most metal refiners put the ammonium hexachloroplatinate in a melting crucible and use a torch or an induction furnace to apply heat. and there we go, purified platinum from laboratory chemical waste. you can see the porous sponge of platinum. i preweighed this vial and so we see we've only produced 337 mg of platinum metal. at current platinum prices that's about $10. now i know a lot of your are going to complain that this refining process was a waste of money
but the point was to explore the science. all these reactions could easily be scaled up to economical levels with enough platinum waste. i think there is more metal in the leached residue that could be accessed by further incineration, but i didn't have time to recover it. now i wouldn't even need a second incineration if i had performed the first one longer. i stopped early because i saw the nickel crucible oxidizing and i didn't want to contaminate my platinum with too much nickel. once i get a proper porcelain crucible this shouldn't be a problem. although i won't be posting videos on that. nonetheless, for a chemist, this is a useful quantity of platinum. so that's how you recover platinum from laboratory chemical waste and separate out the other base metals and organic residues.
this process assumes you have lots of impurities and don't know what they are. successively removing impurities with each step until we get to platinum. you can skip certain steps and save time and money if for example you're certain you don't have base metals or if you don't have any other precious metals. i hope this video was helpful for you. special thanks to my patrons on patreon for supporting me and making expensive science videos like this possible. now if you would like to join them you can find my patreon page in the video description. i really appreciate any and all support.
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